14.7v on stock lead battery?

[saywhaaat]

Hello everyone, I’m designing my v1 12v system for my 06 Tacoma TRD. I have an older platinum die hard AGM 31M that I’m using as my 2nd battery that I’ve used for a few years as my camping battery. I plan on using a Blue Sea ACR to link the alternator charge. Knowing the AGM needs a higher voltage I picked up an HKB voltage booster as well. I would really like to get this build going before I have to drop more mula on a new house battery, but will the stock lead batteries do alright with the boosted voltage? I know on my CTEK it’s boosts the voltage for cold charging, but will the house battery hold up if the charge is constantly around 14.7?

 

[jonyjoe101]

from what I read the diehard platinum requires 14.7 volts to fully charge and they prefer to be charged at high amps. It should be good as long as you don't leave the charger connected 24/7 at 14.7 volts. For longterm trickle charge you need something like 13.8 volts.
I have a small 27ah agm fullriver full throttle (9 year old battery) I'm using it as a start battery but I have to top it off to 14.7 volts with a dc-dc converter every day. The alternator only charges to 14.4 volts. Without the dc-dc converter after about a week I start getting slow cranks, where the battery struggles to start the engine. Keeping the battery topped off to 14.7 gives me a powerful start every morning.

 

[KenC]

Buy a 300 watt cigarette lighter inverter (say $30) for the Tacoma and plug the CTEK in when charging was needed.

 

[saywhaaat]

from what I read the diehard platinum requires 14.7 volts to fully charge and they prefer to be charged at high amps. It should be good as long as you don't leave the charger connected 24/7 at 14.7 volts. For longterm trickle charge you need something like 13.8 volts.
I have a small 27ah agm fullriver full throttle (9 year old battery) I'm using it as a start battery but I have to top it off to 14.7 volts with a dc-dc converter every day. The alternator only charges to 14.4 volts. Without the dc-dc converter after about a week I start getting slow cranks, where the battery struggles to start the engine. Keeping the battery topped off to 14.7 gives me a powerful start every morning.

that is what the hkb booster is. It replaces the alternator fuse and boosts alternator voltage by .5 for that exact reason

 

[BobInTheAspens]

Please take temperature into account! Otherwise you will quickly destroy your battery. It is rare to harm a battery by overcharging, but very easy to destroy one by undercharging. 14.7 v is only right when your battery is a 50 degrees F!

Here is a table of charge voltages and battery temperatures. Note that flooded and AGM batteries require the same charging voltages. (There is a lot of misinformation about charging, even from the manufacturers)

Battery
Temp -- Charge Voltage
122 F -- 13.80
104 F -- 13.98
86 F -- 14.19
77 F -- 14.34
68 F -- 14.49
50 F -- 14.82
32 F -- 15.24
14 F -- 15.90

My 2008 4Runner, with a voltage booster, charges between 13.8 and 14.7 volts depending on the temperature. That seems to work well. It came from the factory set to 13.4 - 13.8. That was typical for Toyota, and will destroy your battery quickly.

Note that these numbers are for when your engine is running. If you hook up a wall charger at home, the numbers need to be lower, and you need to be careful not to overcharge. Consider buying a plug-in charger that is designed for AGM batteries, such as the Optima one. It will do a good job on both AGM and flooded batteries, and won't overcharge.

Lastly, get a good digital voltmeter to install where you can see it while your drive. And watch it! Better still, buy a Scanguage, and watch your transmission temperature and water temperature as well.